High-frequency inductor block



Nov. 7, 1950 J. B. WADHAMS 2,528,714

HIGH-FREQUENCY INDUCTOR BLOCK Original Filed Jan. 24, 1944 Y; T iff-in IHIHHEIILJ? 7/ fia 7 I G' 6 INVENTOR.

J/IMEs 8. Maw/4M3 Arroqzvsys Patented Nov. 7, 1950 HIGH-FREQUENCY INDUCTOR BLOCK James B. Wadhams, Cleveland, Ohio, assignor to The Ohio Crankshaft Company, Cleveland, Ohio, a corporation of Ohio Continuation of application Serial No. 519,559, January 24, 1944. This application October 22, 1949, Serial No. 122,915

8 Claims. (Cl. 219-47) This invention relates to inductors for hi hfrequency induction heating and, more particularly, to an inductor and a method for increasin the input impedance of the inductor on the power source and controlling the loading of the inductor when coupled with its workpiece on the power source.

The present application is a continuation of my copending application, Serial No. 519,559, filed Januar 24, 1944, now abandoned.

r In the field of high-frequency induction heating, it is conventional to employ an inductor formed from a slab of high-conductivity material, such as copper, having a workpiecereceiving bore or opening extending from one side to the other. A slot extends-from the bore to the edge of the slab, providing on each side of it a pair of parallel, close-spaced, fish-tail leads which are connected to a suitable source of highfrequency electric power. Such sources may consist of rotary-type, high-frequency generators or electronic-type power sources.

Alternatively, the inductor may comprise a length of a conductive material shaped into a loop to form the workpiece-receiving opening and with the ends extending away from the loop in close-spaced parallel relationship.

High-frequency electric currents from the power source, whichever type may be employed, circulate down the leads of the inductor and around the workpiece opening, inducing con centrated, high-frequency currents to flow peripherally around the portion of the workpiece within the opening, which currents heat the portion very rapidly to a desired .elevated tempera- I ture.

The axial width of the workpiece in which the concentrated currents flow is primarily a function of the ratio of the workpiece-opening diameter to the workpiece diameter and the thickness of the inductor or, in other words, the axial length of the workpiece opening.

'As the ratio of the workpiece-opening diameter and workpiece is increased, the width of the pattern on the workpiece is increased and vice versa. If the length of the workpiece opening is increased, the width of the heat pattern on the workpiece also increases and vice versa.

These same factors also have a direct efiect on the input impedance of the inductor and of the loading of the inductor with the workpiece in position on the power source.

If the ratio of the workpiece-opening diameter to the workpiece diameter is increased, the loading decreases and vice versa. If the thickness of the block or the length of the workpiece open,

thus obsoleting the old transformer.

inductor is too low so that the power source is overloaded. Prior to this invention, complete reconstruction of the inductor was required in order to vary the input impedance, or com- I promises in the heat pattern were necessary.

Inductors of this type are normally always connected to their power source through an impedance-matching device or transformer. and, in some cases, the effects of this overloadingor low input impedance of the inductor can be cor rected by changing or increasing the impedance ratio of the matching transformer. However, at times, changing the impedance ratio of the trans? former is not feasible. Insome cases, where a fixed ratio transformer is already installed, a new transformer with a difierent ratio is required, In other cases, it is not feasible or electrically eflicient to obtain a greater ratio of impedance transformation. This is particularly true with electronictype power sources which have an internal impedance on the order of a thousand ohms .or more. Matching such a power sourceto the extremely low impedance of a properly loaded inductor is exceedingly diflicult and sometimes cannot be done even though a single-turn secondary transformer .-is employed.

Another difficulty has been where a pair of inductors are employed which are to 'be electrically connected either in parallel or in series with the same power source. Here the inductors, even though of identical dimensions, may have difierent input impedances and will not draw the same amount of power from the power source.

The present invention contemplates an inductor construction and method for individually enabling adjustment of the input impedance of a high-frequency inductor whereby the above referred to difiiculties will be alleviated. The invention contemplates an inductor having a workpiece-receiving opening and a pair of parallel, close-spaced, fish-tail leads which are adapted to connect to a power source so that high-frequency currents may be flowed around the opening. However, the opposing surface or heating with h gh frequency currents which I comprises flowing high-frequency currents-from a high-frequency power source in close-spaced parallel relationship, then in substantial-spaced relationship about an area void of electricallyconductive material, then in close-spaced relationship and then in a loop around a space substantially filled with a workpiece to be heated whereby to induce heating currents in the workpiece. I

The inductor block may'bemade more or less hollow and the waucr theblock defining the workpiece-receiving "opening may be provided witha plurality of openings communicating with thehollow interior of the block and quench water may be projected through-theseopenings: onto the heated workpiece. However, "the recess formed in thewalls of the fish-tail leads are im- 4 mately on the line 3-3 thereof but without the workpiece in position;

Figure 4 is a cross-sectional view of Figure 2 taken approximately on the line 44 but without the workpiece in: position;

v Figure5 is an elevationalv1ew-of an inductor block showing .a modified embodiment of the invention wherein means are provided for adjustingthe area of the input impedance adjusting opening;

- Figure: 6 is a sectional view of an inductor 1 taken approximately on the line 66 of Figure 5; and

.. Figure '7 is a sectional view taken approximately on the line 7-4 of Figure 5.

. Referring :now to the drawings, Figure 1 shows a conventional high-frequency, induction-heating arrangement and is shown for the purpose of pervious and donothaveopenings communicat- 1 ing with the interior or th-block,*the purpose beingiso that'quench water will not flow into the recess and be wasted during the quenching operation.

Theiinvention" also contemplates an inductor having a control opening in the leads with means for varying its area.

' The principal object: of. the present invention is to provide an *inductoryhavi'ng means for regulating its loading on a power circuit other than varying'the dimensions of'the workpiece-receiving opening.

'Anotherjobject'of'the invention is to provide an inductor block of the quench-through-theblock type havinga recess in the opposed surfaces of the fish-tail leads toincrease the input impedance of the ind ctor on'a power source.

.Still a further obiect is to provide a high-frequency 'inductor of the quench-through-theblock type Whichmay have the'workpiece-receiving, openingconstructed to the optimum dimen sions for the desired'heating of a workpiece and still efiect a desired loading on a power source.

"Another object has been'to provide a simple means for controllingthe input load impedance and, thus, the loading of an inductor on apower source so that'heating-of a workpiece can be obtained in the shortest possible time and with the 1east"powerfrom the source.

.The invention will be specifically set forth and defined in the appended claims. The invention, of course, may take physical form in'a number of difierent-appearing embodiments and preferred embodiments of the invention'will be described in detail in th s specification and illustrated somewhat diagrammatically in the accompanying drawings which form apart of this specification, and wherein: Figure 1 shows a conventional induction-heating circuit. including a power source, an impedance=matching transformer and a high-frequency inductor of the quench-through-theblock type; Figure 2 is a view similar to Figure 1 but with thepresent invention applied thereto;

Figure'3 is a view of Figure 2 taken approxi more clearly illustrating the present invention. In Figure 1, there is shown a high frequency power source- A, an impedance-"matching tr'ans-' former'B and an inductor block C electrically connected for thepurposeiof heating a workpiece'D. The power -s'ource A mayl be of any conventional type capable of supplying highsfrequen'cy, high-voltage, electric? power such as 1 az rotating generator or. an: electronic-valve, high frequency oscillator.

The inductor block is provided with a workpiece-receiving opening 10 and 1 the workpiece-iD is shown -in-='cross :se'ction positioned in this opening. 1 1 The block C has a longitudinal slot" 20 communicating with-'th'e workpiece opening 7 I tl- 'and dividing-the block on one'side -of theopening into defined by close spaced "parallel sides '23, 24 of the leads 2!, fiz respectivelyf*The workpiecereceiving opening is de'fined bya wall 27. This wall is provided-witha plurality of" openings 28 which communicate with a hollow interior 29 of the inductorblo'ck; -Water is circulated into the hollowinterion29'under pressure through suit-.

able water connections-Wand is'ejected through the openings '28 at high velocitiesonto the heated surfaces of theworkpiece D to rapidly .coolthe workpiece after' -it has-been heated bythe highfrequency currents. This quench arrangement is more clearly disclosed in-thepatent' to Denneen, et al.,-' No.' 2;170',I30:dated- August22,1939.

A condenser I 2 is also shown-connected in parallel with' the--power source A, the -purpose of which is to adjust the power 'i actor demand on the power source A if a rotating-type generator I is -employed, or to adjust 'theffrequency of the power source ii-an electronic'power source is employed. In the latten eventythe primary coil I3 of the transfo'rmer B may be I employed as the oscillatory tank circuit of the electronic power flowing therein. With the block as shown in Figure 1, there is only one way of increasing the input impedance of the inductor block sothat theloading on the power source may be decreased; that is, Without varying the impedance ratio of the transformer B. This may be done only by decreasing the length of the work-piece opening or in increasing the diameter of the workpiece opening, Or both. As previously stated, varying thedimensions of the workpiece opening may adversely affect the heat pattern in the workpiece D. This is particularly so where a very narrow heat pattern is desired. Also, if the inductor has been carefully designed, there is generally insufficient metal about the opening to permit changing the dimensions to any appreciable extent.

The present invention provides a means for increasing the input impedance of an inductor block without in any way altering the shape of the workpiece-receiving opening. shown in Figure 2, the walls 23', 24 forming the slot are made to have an appreciable thickness in a direction laterally away from the slot 20.

In the embodiment shown in Figure 2, the walls 23 and 24 are each provided with oppositely disposed, semicircular openings which, in conjunction, form an input impedance control opening 33. Dependent upon the dimensions of the opening selected, the input impedance of the inductor block may be adjusted to any desired value. As shown, the walls defining the opening are impervious to the interior of the inductor block so that no quench water will flow therethrough while the workpiece D and the workpiece-opening H] are being quenched. Also, the opening 33 should preferably be kept clear of electricallyconductive material in order that its effect of an increase in the input impedance of the inductor block will be a maximum. In some instances, if thehole is made too large, it is possible that such material may be placed in the opening 33 to decrease the effect of the opening.

While the opening 33 is shown as circular, it need not be and may take any other form, such as rectangular, or there may be a plurality of such openings provided. Also, the recesses need not be oppositely disposed or' only one need be provided.

The inductor shown in Figure 2 is shown in greater detail in Figures 3 and 4. It will be appreciated that if a solid block of copper is provided from which the inductor is made, the formation of the interior passage 29 may involve some difficulty. Figure 3 shows one way in which this may be accomplished. The interior 29 is milled out in a conventional manner and a cover 46 of the shape to fit over the milled opening 29 is provided, this cover 40 being soldered or brazed in position. Obviously, the hollow interior could 'Thus, as .1

In the inductor of Fig ures 5 through 7, a modified rectangularform prises two halves or legs 66 and 6| which are adapted to be attached to terminals l5 and I6 of the transformer B. The inductor is provided with two openings, opening 64 ordinarily being a bore of suitable diameter to receive the part to 'be heated. The other opening 65 ordinarily is for the purpose of permitting the desired ratios of work diameter to bore diameter and bore di-' ameter to bore length while still having the correct input impedance for the desired power. In

selecting an inductor, one having the correct bore is usually available, but the dimension ratios of such an inductor may be very unfavorable to efficient loading. To provide the desired "loading, opening 65 is provided and this opening is made adjustable in area.

To accomplish the adjustability of opening 65, the inductor members and 6| are cut away to provide an elongated space between them. A block of conducting metal 66 is inserted in the open end of this elongated space to bridge this space and to provide a continuous conducting peripheral wall for opening 65. faces of the space are provided with longitudinal grooves 61 to receive guide elements on block 66 to guide the block when it is moved longitudinally of the space to vary the size of opening 65. The movement of the block is accomplished by screw 68 which threadedly engages the block. This screw is held axially by clamp belt 69 through which it passes. Collar 10 and head H of the screw engage opposite sides of the bolt to prevent axial movement. When it is desired to change opening 65, the nut 12 of clamp bolt 69 is loosened to release pressure on the opposite sides of block 66 and screw 68 is turned to bring this block to a desired new location after which nut 12 is tightened to insure good current-conducting contact between the block and the inductor members.

By providing spring '13, the pressure exerted on block 66 by the members 60 and 6| is such as to permit this block to be moved along these members while maintaining current-conducting contact therewith, thus eliminating the necessity of loosening nut 12. For convenience, a scale may be provided along a face of one of the inductor members, cooperating with a line scribed on block 66. This scale may be calibrated to read in any desired units such as input impedance for a given condition of loading.

It willbe observed that by the form of the inductor members 66 and 6| and by the form of block 66, the form of opening is established and that, for certain operations, this opening can be employed to receive the workpiece to be heated while bore 64 is employed to match the inductor to the work. Members 62 and 63 are so supported as to permit of such movement of members 60 and 6| as is necessary for the movement of block 66.

The opening 65 is shown remote from the power source. It could be po itioned otherwise than as shown. The walls defining the workpiece opening 64 are shown as imperforate. They could be provided with quench openings, if desired.

In constructing an inductor block of the type shown in Figures 1 to 3, the thickness of the block is chosen to correspond to the desired length of the workpiece opening l0 so as to produce the desired width of heat pattern when taken into consideration withthe diameter of the opening in relation to the diameter of the workpiece to be heated. The method of de- The opposite termining the size of'this hole is well known to those skilled inthe art and; will not be further detailed here. Sufiiceit to sa that when the dimensions of the opening are chosen and the inductor block is connected-to a power source as shown in Figure l and the workpiece placed in the. opening ii), the input impedance of the inductor block will oftentimes be so low that it is impossible to properly match the inductor and its load to the power source with conventional impedance-matching equipment or without replacing the existing impedance-matching equipment with new equipment; The effect of this low input-impedance is to load the power source beyond its power output capability. In the case of rotating equipment, overheating of the power source may result. In the case of electronic equipment, the result may be an extreme loss in efliciency and decrease in the power output evenas shown in Figures 2, Sand 4, the-amount of recessing being required depending entirely upon the'amount of increase'in the input impedance oftheinductor block necessary to efiect the properloading on the power source.

With the inductor block shown in Figures to.

7,-it" is simpl necessary to adjust the position of the block 66, thereby adjusting the area of the opening 55 and effecting the desired input I impedance variation.

'With the inductor of Figure 1, the high-frequency currents tend to concentrate almostuentirely on the surfaces of the leads 2!, 22' facing the .slot 283 until they reach the opening l5 when they divide to flow around the opening but still crowded close to the-surface of the opening and,

about an area having no electrically-conductive material therein. Then the currents flow in close-spaced parallel relationship for a distance and then again divide to flow around the walls of the workpiece opening and induce high-frequency currents to flow in the workpiece. By dividing the current flow, the input impedance can be increased to any desired amount.

Thus, it will be seen that embodiments of the invention-have been described which accomplish the objectives set forth hereinabove as well as others and which permits a method of current flow and an inductor block wherein the input impedance may be readily adjusted so that an inductor may have an optimum heating pattern on'a workpiece while still providing the optimum loading on a power source.

Having thus described my invention, I claim:

1. In an inductor adapted to heat an article by high-frequency current being supplied thereto, said inductor comprising an inductor block having an opening adapted to receive the article in closely-spaced relation with a surface of the opening, a control opening adjacent V to the article-receiving opening, the control opening be- 'ingconnected to the article-receiving opening by a relatively narrow slot and serving as means", for increasing the input-impedance of the in:

ductor on the power source, and means for vary-- ing the area of the control opening whereby to change said input impedance.

2. An inductor adapted to heat an article by high-frequency current being supplied thereto, said inductor comprising two closely-spaced, substantiallycomplementary ing to provide openings through the inductor, one

of said openings being adapted to receive in; closely-spaced relation an article to be heated,

the other opening lying adjacent to the article,- receiving opening and beingadapted to regulate the input impedance of said inductor, and means for varying the size of the last said opening, said varying means comprising a movable member bridging a part of the space between the inductor segments, the movable member serving as a conductor joining parts of the segments.

3. An inductor adapted to heat an article by high-frequency current being supplied thereto,

said inductor comprising two closely-spaced, substantially-comple-mentary segments, adjacent parts of said segments having recesses cooperating to provide openings through the inductor, one

of said openings being adapted to receive in closely-spaced relation an article to be heated, the other openinglying adjacent to the articlereceiving openingiand being adapted to regulate the input impedance of said inductor, and means for varying the size of the last said opening, said varying means comprising a current-conducting -memher movablealong the space between the segments, and serving as means for bridging a part of the space between the segments, means for selectively positioning the bridging means to accurately control the size of the last said opening, and clamping means to deflect the aforesaid segments into current-conductingengagement with the bridging-means to complete a series circuit for high-frequency heating current through the bridging means and through the ".segments of the inductor.

4. In an inductor adapted to heat an article by high-frequency current being supplied thereto,

an article opening adapted to receive the article.

in closely-spacedrelationship with a surface of the opening, a control opening adjacent to the article-receiving opening and having a movable wall surface, the control opening being connected to the article-receiving opening by a relatively narrow slot and serving as means for increasing the input impedance of the inductor on the power source, and means for moving the wall surface'to varythe size of the control opening whereby to change said input impedance.

5. A high-frequency inductor comprising an electrically-conductive member having a workpiece-receiving opening therethrough and including a wall defining said opening with a plurality of quench openings extending into an interior passage of said member, said member also including a pair of close-spaced parallel arms having close-spaced surfaces defining a slot communicating with said workpiece opening, at least one of said surfaces being recessed with the recess void of electrically-conductive material, whereby to increase the input impedance of said inductor over that without said recess, the walls defining said recess being imperforate to the interior passage of said member.

6. The method of manufacturing a high-frequency inductor. block normally having a work:

segments, adjacent parts of said segments having recesses co operat-r piece-receiving opening and a pair of closespacedparallel leads adapted to connect to a source Qfhigh-fre uency power which comprises forming said workpiece-receiving";opening to have a diameter and length such astij provide a desired heating pattern on a workpiece and subsequently adjusting the input impedance of said block by providing a recess in at least one of the close-spaced surfaces of said leads until the input impedance is increasedthe desired amount 7. The method of increasing the input impedance of a high-frequency inductor having a workpiece-receiving opening of fixed and unchangeable dimensions and a pair of close-spaced parallel leads adapted to be connected to a source of high-frequency power which comprises providing a recess void of electrically-conductive material in one of the opposing surfaces of said leads, the recess having dimensions such as to increase the impedance by the desired amount.

8. The method of adjusting the loading of a high-frequency inductor on an electronic power REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,271,916 Denneen et al. Feb. 3, 1942 2,353,130 Dravneek July 11, 1944 2,402,508 Strickland June 18, 1946 

